Flocculation
Please see article, Flocculation, at engineering.wikia at link (http://engineering.wikia.com/wiki/Flocculation) The process of Flocculation can be described in two ways depending on the location where it is used. 1. Flocculation as seen by engineers. 2. Flocculation as seen by chemical engineers. Flocculation as seen by engineers Flocculation is a process where a solute comes out of solution in the form of floc or "flakes." The floc may then float to the top of the liquid, settle to the bottom of the liquid, or can be readily filtered from the liquid. The floc operation may be expedited by adding some chemicals. Uses Flocculation is widely employed in the :1.initial purification of drinking water, :2. a) treatments of sewage water, :: b) treatment of Stormwater and :: c) treatment of other industrial water streams, :3.Waste water, :4.In brewing and fermentation operations. In utility power stations, raw water treatment may start with a flocculating process. Process explained Flocculation is reversible as opposed to with agglomeration and coagulation1. For emulsions, flocculation describes clustering of individual dispersed droplets together, whereby the individual droplets do not lose their identity2. Flocculation is thus the initial step leading to further aging of the emulsion (droplet coalescence and the ultimate separation of the phases). In civil engineering and in earth sciences, flocculation is a condition in which clays, polymers, or other small charged particles become attached and form a fragile structure, a floc. In dispersed clay slurries, flocculation occurs after mechanical agitation ceases and the dispersed clay platelets spontaneously form flocs because of attractions between negative face charges and positive edge charges. In biology, the process is used to refer to the asexual aggregation of microorganisms, most commonly brewing yeast at the end of a brew. Flocculation as seen by chemical engineers Flocculation, may form by polymers forming bridges between the flocs. and binding the particles into large agglomerates or clumps. Bridging occurs when segments of the polymer chain adsorb on different particles and help particles aggregate. An anionic flocculant will react against a positively charged suspension, adsorbing on the particles and causing destabilization either by bridging or charge neutralization. In this process it is essential that the flocculating agent be added by slow and gentle mixing to allow for contact between the small flocs and to agglomerate them into larger particles. The newly formed agglomerated particles are quite fragile and can be broken apart by shear forces during mixing. Care must also be taken to not overdose the polymer as doing so will cause settling/clarification problems. Anionic polymers themselves are lighter than water. As a result, increasing the dosage will increase the tendency of the floc to float and not settle. The term is also used in colloid chemistry to refer to the process by which fine particulates are caused to clump together into floc. Once suspended particles are flocculated into larger particles, they can usually be removed from the liquid by sedimentation, provided that a sufficient density difference exists between the suspended matter and the liquid. Such particles can also be removed or separated by media filtration, straining, or floatation. When a filtering process is used, the addition of a flocculant may not be required since the particles formed by the coagulation reaction may be of sufficient size to allow removal. The flocculation reaction not only increases the size of the floc particles to settle them faster, but also affects the physical nature of the floc, making these particles less gelatinous and thereby easier to dewater. Initial purification of drinking water Initial purification of drinking water is the removal of contaminants from untreated water to produce drinking water that is pure enough for its intended use, most commonly human consumption. Substances that are removed during the initial process of drinking water treatment include algae, bacteria,and minerals such as iron, and man-made chemical pollutants. Treatments of sewage water Treatment of Storm water Treatment of waste water Treatment of water in brewing yeast Treatment of other industrial water streams Here it mainly refers to the raw water input to the utiity power stations using conventional boilers and steam turbines. This raw water input to boilers may be from bore wells, from open wells, from dams or flowing rivers. The type of quality of water requirement at various stages of the process do vary. :(To be continued-Other chemical engineers may help)